Bartholemew "Bat" Masterson was born to a working-class Irish family in Quebec, Canada, but he moved to the Western frontier as a young man and quickly distinguished himself as a buffalo hunter, civilian scout, and Indian fighter on the Great Plains.

In July 1872, Masterson was hired by a subcontractor named Raymond Ritter to grade a five-mile section of track for the Atchison, Topeka & Santa Fe Railroad. Ritter skipped out without paying Masterson all of the wages to which he was entitled. It took Masterson nearly a year, but he finally collected his overdue wages from Ritter--at gunpoint.

He was engaged in buffalo hunting on June 27, 1874, when he became an involuntary participant in one of the Wild West's most celebrated Indian fights: a five-day siege by several hundred Comanche, Kiowa and Cheyenne warriors led by Quanah Parker at a collection of ramshackle buildings in the Texas panhandle known as Adobe Walls. Masterson was one of just 28 hunters who defended the outpost during the attack. The Comanche suffered heavy losses during the battle, with reports ranging from a low of 30 to a high of 70. The defenders of Adobe Walls lost only four men, one of whom shot himself by accident.

Masterson's first gunfight took place on January 24, 1876, in Sweetwater, Texas. He was attacked by a soldier, Corporal Melvin A. King, allegedly because he was with a woman named Mollie Brennan. Brennan was hit by one of King's bullets, possibly by accident, and died from her wounds. King was also killed. Masterson was shot in the pelvis but recovered.

On November 6, 1877, Masterson was elected county sheriff of Ford County, Kansas, by the narrow margin of three votes. Within a month of his election, Masterson's brother Ed replaced Larry Deger as city marshal of Dodge City, Kansas, so together the Masterson brothers controlled the city and county police forces. The tandem law enforcement effort came to an abrupt end, however, when Ed was shot and killed in the line of duty on April 9, 1878.

On October 4, 1878, a variety actress named Dora Hand, known professionally as "Fannie Keenan," was shot and killed by James Kenedy, the son of a wealthy Texas cattleman. Masterson's posse, which included Wyatt Earp , captured Kenedy the following day after Masterson shot him in the left arm, and other posse members killed his horse.

He took an interest in prizefighting and became a leading authority on the sport, attending almost every important match and title fight in the United States from the 1880s until his death in 1921.

On February 8, 1881, he left Dodge City and joined Wyatt Earp in Tombstone, Arizona Territory, where he met boxing promoter Luke Short for the first time. Earp, Short, and Masterson worked together as faro dealers, or "look outs", at Tombstone's Oriental Saloon.

Masterson was appointed city marshal of Trinidad, Colorado, on April 17, 1882. He had hardly settled into his $75-a-month marshal's job when Wyatt Earp requested his help to prevent the extradition of Doc Holliday from Colorado to Arizona, fearing his friend wouldn't get a fair trial for the murder of Frank Stilwell, who had killed Wyatt's brother Morgan. Masterson took his case directly to Colorado Governor Frederick W. Pitkin, who allowed him to take Holliday to Pueblo, where he was released on bond two weeks later.

Jefferson Randolph "Soapy" Smith II gained notoriety through his "prize soap racket," in which he would sell bars of soap with prize money hidden in some of the bars' packaging in order to increase sales. However, through sleight-of-hand, he would ensure that only members of his gang purchased "prize" soap. At one point, Soapy controlled all but one of the 40 gambling saloons in Creede, Colorado--the only exception being the Denver Exchange, which was managed by none other than Bat Masterson. In 1889, both men were involved in an election scandal involving fraudulent ballots.